For several years, cryotherapy was de rigueur among pro athletes looking to recover quicker from tough workouts. Then word got out, which prompted a proliferation of cryo bars and boutiques marketed to the rest of us.

Whole-body cryotherapy essential flash-freezes the body with liquid-nitrogen vapors. You enter a tanning-booth-like chamber, dressed in skivvies and mittens, and endure temperatures of –200 to –300 degrees (10 times colder than ice) for three minutes. Your body goes into shock, prompting the fight-or-flight response. Fearing that your heart and vital organs are about to freeze, it sends blood racing from the extremities to the core to keep it warm. The blood is treated to a fuller infusion of oxygen from its extra time in the lungs and heart. Then, when that oxygen-saturated blood returns to the extremities, it reduces sports-induced inflammation and speeds tissue repair in the muscles. Or so cryo boosters say.

Scientists are dubious. For starters, they’re not even sure what happens to the body during cryotherapy. As for studies, a research review from the Cochrane Library found that there is not enough evidence to validate its use. And research from the International Journal of Sports Physiology and Performance found that it didn’t significantly boost muscle strength or cardio endurance, as some makers promise.

But here’s the biggest knock against cryotherapy: “You don’t always want to stop that inflammation response after a workout,” says Michael Fredericson, M.D., an orthopedic surgeon at Stanford University ­Medical Center. When you exercise, muscle tissue breaks down, activating the body’s healing response. Yes, that causes soreness, but it also means the growth of healthier, stronger tissue. “If you blunt that response, you’re probably not getting as much benefit from the workout,” says Fredericson.

Those who swear by cryotherapy could be experiencing the placebo effect. Their exhilaration might not be top-speed muscle repair but the same rush that a dip in an ice-cold pool provides, says Fredericson. Speaking of which, there’s nothing to suggest that a cryo chamber is more effective than an ice bath, which sports doctors recommend sparingly, says Dominic King, a sports medicine physician at Cleveland Clinic. Ice is best for acute injuries, such as sprained ankles, to reduce swelling and pain, King says. As for whole-body treatments, we’re still waiting on some cold, hard facts.